1. Field of the Invention
The present invention relates to a vibration isolating apparatus which prevents transmission of vibration from a vibration generating member and is applicable to a case in which transmission of vibration from, for example, an engine disposed on a vehicle is prevented.
2. Description of the Related Art
For example, a structure is known in which a vibration isolating apparatus serving as an engine mount is disposed between a vehicle engine which is a vibration generating portion and a vehicle body which is a vibration receiving portion, and vibration generated by the engine is absorbed by this vibration isolating apparatus and is prevented from being transmitted to the vehicle body.
Namely, an example of this vibration isolating apparatus includes the one having a structure in which a main liquid chamber and an auxiliary liquid chamber are provided inside and these liquid chambers are communicated with each other by a restricting passage serving as an orifice. When the disposed engine is operated so as to generate vibration, the vibration is absorbed or damped by liquid within the restricting passage which communicates these liquid chambers due to liquid-column resonance or the like as reduced dynamic spring. Transmission of the vibration is thereby prevented.
On the other hand, the range of vibration frequencies becomes large due to the wide range of operating states of an engine. Accordingly, in recent years, a vibration isolating apparatus which has restricting passages having different lengths and inner diameters has been proposed in order to maintain vibration isolating characteristics against each of vibrations of such wide range of frequencies. Alternatively, a vibration isolating apparatus has been proposed in which a membrane made of a rubber is provided on the opposite side of a partitioning member, which partitions a main liquid chamber and an auxiliary liquid chamber, with respect to the main liquid chamber, deformation ability of this membrane is used so as to reduce the dynamic spring constant of vibration having a high frequency range, and the vibration having a high frequency range is thereby reduced.
However, when vibration having a low frequency range is generated at the same time that the vibration having a high frequency range is generated, it is difficult for any of the above-structured vibration isolating apparatuses to sufficiently reduce the vibrations.